Red bumps on skin

For the past 2 years my 5 year old has had red bumps appear on his skin.  They are usually raised and stay for weeks.  Eventually they begin to smooth out and turn a brown color.  After several months the area will return to normal color.  It started with one on his leg and over the past few years has had at least 15 of them in different areas of his body.  Doctor thought they were mastocytosis and said they would go away as he ages.  Wondering if anyone else has experience with this?

Thank you